Tone shaping circuit



June 19, 1951 F. M. SCHMIDT 2,557,759

Toma SHAPING CIRCUIT Filed June 1, 1949 TavEG'f/vsfms 'Patented June 19, 1951 TONE SHAPING CIRCUIT Francis M. Schmidt, North Tonawanda, N. Y., as-

signor to The Rudolph Wurlitzer Company, North Tonawanda, N. Y., a corporation of Ohio Application June 1, 1949, Serial No. 96,546

6 Claims. l

This invention relates to frequency discriminating networks and more particularly to tone shaping circuits incorporated in an amplier used in conjunction with an electronic musical instrument such as an electronic organ.

In musical instruments in general it is often desirable to emphasize or to suppress certain qualities of musical tones. In electronic organs, for instance, it is desirable to accentuate the output of certain regions in the frequency spectrum for one group of tone generators while it is desirable to emphasize the output of other groups of tone generators in other regions.

Among the important objects of this invention is the selective shaping of the outputs of various groups of tone generators in an electronic organ.

Another object of this invention is to provide means by which the amplitude of certain musical tones may be altered in accordance with the requirements of the different acoustical phenomena encountered in various electronic organ installations.

Another object of this invention is to provide selective emphasis or discrimination of groups of musical tones in an electronic organ to agree with individual taste.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in conjunction v with the accompanying drawings in which:

Fig. 1 is a fragmentary partially schematic end view of an electronic organ in which this tone shaping circuit may be utilized;

Fig. 2 is a schematic wiring diagram of a preferred embodiment of the tone shaping circuit; and

Fig. 3 is a family of curves illustrating the relative output wave forms of the tone shaping circuit described.

Fig. l is a fragmentary end view of an electronic organ l having a plurality of hand actuated keyboards or manuals 3 and a pedal keyboard 5. A plurality of tone generators 1 are preferably of the vibrating reed type described by ,A

Hoschke in his Patent No. 2,915,014 in which the changing capacitance between a vibrating metallic reed and a plurality of adjacent screws gencrates a musical tone. A blower 9 supplies air to a wind chest Il and pallet valves 13 admit air to the tone generators from the wind chest. The output of the tone generators 1 is connected to an amplifieri5 which includes the tone shaping circuit which is the subject of this invention. The amplifier also has associated with it a volume (Cl. S11-1.12)

control I6 actuated by a foot pedal l1. The interconnections between the tone generators and amplifier are controlled by a coupler board I9 and a second coupler board 2l may control the operation of the pallet valves in response to the operation of the various keys. A bank of stop tablets 23 may control the operation of the coupler boards I9 and 2|.

As described in the aforementioned patent to Hoschke, the reeds comprising the tone generators may be prevoiced to give effects such as flute tones, string tones, etc. One group of reeds prevoiced to simulate flute tones may be electrically connected in parallel as is diagrammatically represented at 25 in Fig. 2 and connected to a positive source of potential and to ground through a resistance capacitance network 21. The adjacent elements which in conjunction with each of the vibrating reeds comprises a series of capacitors may al1 be connected in parallel as is diagrammatically illustrated at 29 in Fig. 2. In like manner other groups of similar prevoiced reeds are connected in parallel as the pedal reeds 3|, viola reeds 33, and diapason reeds 35, and they are likewise connected to a positive source of potential and to ground through resistance capacitance networks 21. The cooperating capacitance elements of the last named groups are connected in parallel groups and are illustrated diagrammatically in Fig. 2 as 31, 39 and 4I, respectively.

The outputs of the flute, pedal and diapason banks of tone generators are yconnected through suitable isolating and voltage dividing networks to an amplifier tube 43. The networks comprise a plurality of resistors 45, 41, 49, 5l and 53 and a capacitance 55, all of which in combination with the varying capacitance of the tone generators determine the alternating current voltage impressed on the grid of the amplifier tube 43. The amplier tube 43 is provided with a cathode bias resistor 51 and cathode capacitor 59 in the usual manner and plate potential is supplied through a plate load resistor 6l from a suitable source of positivedirect current potential.

The output potential of the viola tone generators is connected to the grid of a second amplifying tube 63 through aresistor 65. A resistor 61 is connected between the viola tone generators and the resistor 55 and to ground. The resistors 65 and 6"! provide isolation and determine the value oi potential applied to the grid of the tube 63. A cathode resistor 59 and a capacitor 1I in parallel therewith provide cathode bias for the amplifier tube 53 in the usual manner. Plate potential for the tube 53 may be supplied through the resistor d i3 which may be connected to the same source of positive direct current potential.

The outputs ci the two amplifier tubes i3 and 53 are combined through networks to be described later to excite the grid of a combined ampli'er tube l5 which is cathode biased by means or" a cathode resistor 'il and cathode condenser 'E9 connecting the cathode to ground. The output circuit of the tube ii may be conventional and is consequently not shown. A resistor 8l and capacitor t3 are connected in series with the plate of the tube and the grid of the tube 15. The plate of the amplier tube 63 is-also connected to the grid oi the combining amplifier tube l5 by means of a capacitor 35 and resistors El and B9. The plate of the amplifier tube i3 is connected to the grid of the combining amplifier tube l5 through a capacitor Si, resistor 93 and the aforementioned resistor 89. A resistor e5 is connected at one end to the junction between resistors 89 and 93 and at the other end to a resistor @l and capacitor t9. The resistor Sil' and capacitor 99 are connected in parallel and are grounded. A movable tap switch arm lill is connected to the junction between resistors $5 and 'i and selectively engages tap switch contacts w3, |35 and il. The tap switch contact iiS is an open contact and the tap switch contacts 165 and lcl are connected to ground through capacitors m9 and l l l respectively,

Curve A in Fig. 3 is indicative o1" the output response of the amplilier when the grid of the tube 53 is excited. The constants of the resistor Si and capacitor 83 are such as to offer a low impedance to the higher frequencies and a relatively high impedance to the lower frequencies so that the higher frequencies are relatively emphasized.

The bass frequencies in the output circuit of the amplifier tube '33 pass through a low impedance path including capacitance 85 and resistor 8l to the grid of the tube l5 where combined with the output of tube i3 they become essentially a part of curve B which represents the overall amplier response if input is applied to the grid of tube Q3. Curve B likewise illustrates that the circuit comprising resistors and 9i' and capacitors 9s, iS and lll emphasizes the bass irequencies while relatively discriminating against the higher frequencies. It is relatively more difficult to hear the low frequencies at certain volume levels varying to some extent with the installation and consequently the tap switch lili which aids in accentuating the low frequencies may be termed a pedal compensator. Movement of the tap switch arm lill to the higher number tap switch contacts E05 and lill increases the emphasis on the bass as shown 'by curves C andV D and may be preset when the electronic organ is installed.

It is evident that the tone shaping circuit herein described modifies the output wave shape of the tone generators in conformance to desired requirements by selectively accentuating or discriminating against portions or the output tones, the selective pedal compensator or tap switch permitting adjustment of response in accordance with the acoustical requirements of a given location or individual taste.

It is obvious that various changes may be made in the details of construction in the example shown, and I therefore intend to be limited only .by the spirit and scope of the following claims.

I claim: Il. In an electronic musical instrument having a plurality of tone generators each producing a tone of complex quality, a tone shaping circuit comprising a plurality of substantially parallel electronic amplification means, each of said means accentuating certain portions of the complex output of each of said tone generators while relatively discriminating against other portions, and electronic means for combining the outputs 0i said tone generators to form a composite tone.

2. A tone shaping circuit as defined in claim 1 in which one of said substantially parallel amplitying means includes means for relatively eniphasizing the lower frequencies and another of said amplifying means includes means for relatively emphasizing the higher frequencies.

3. In an electronic musical instrument having a plurality of musical tone generators each producing a tone of complex quality, a tone shaping circuit comprising an electronic tube, an electrical network including resistances and reactaiices interconnecting the control element of said electronic tube and some of the tone generators to provide isolation therebetween and determine the alternating current potential applied to said control element, an output circuit for said electronic tube, a second electronic tube and a network connecting said output circuit and the control element of said second vacuum tube, said network including reactances and impedances to relatively emphasize certain frequencies while discriminating against others of each of said complex tone qualities, a third electronic tube connected between some of said tone generators and the control element of said second amplifier tube substantially in parallel with said first ampliner tube, and a second network between the control element of said second tube and the output from said third tube, including resistances and reactances proportioned to emphasize portions of the tone frequencies other than those emphasized by said iirst mentioned network interconnecting said rst and second amplier tubes.

Ll. In an electronic musical instrument having a plurality of musical tone generators each producing an 'output tone of complexquality, a tone shaping circuit comprising a combining ampliiier tube and a plurality of substantially parallel electronic paths interconnecting said combining amplier tube and a plurality of tone generators., means in each of said substantially parallel paths accentuating selected tone frequencies of each of said output tones, and variable impedance means in one of said substantially parallel paths determining the relative extent or accentuation.

5. A tone shaping circuit as described in claim 4 in which the variable means controlling'the extent of accentuation comprises a switch and capacitors of dilerent values connectable into circuit by said switch.

6. In an electronic musical instrument having a plurality of musical tone generators each producing an output tone of complex quality, a tone shaping circuit comp-rising a iirst amplifier tube, a network interconnecting said first amplifier tube and some of said tone generators, a combining amplier tube, a network interconnecting the output of said first amplifier tube and the control element of said combining amplier tube, said ne vork including an impedance branch shunting part of said output to ground to discriminate against selected tones, a second ampliier tube, circuit means connecting the control element of said second amplifier tube to some of. said tone generators, a low impedance path connecting the output of said second amplifier tube to the control element of the combining amplifier tube, and a second path substantially in parallel with said low impedance path, said second path including a reactance element to E emphasize certain tone frequencies.

FRANCIS M. SCHMIDT.

6 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS A Date Number Name 2,340,001 McKellip Jan. 25, 1944 2,429,226 Hanert Oct. 21, 1947 2,481,608 McKellip Sept. 13, 1949 

